syntax - What is different between @+id/android:list and @id/android:list?

Question

I've develop android application, and one question.

As you know, When we use LiveActivity, we must specify @id/android:list for ListView ID.

But, When I use @+id/android:list instead of @id/android:list, it is working fine.

What is different between @+id/android:list and @id/android:list ??

Answer 1

The fundamental difference between @ and @+ is that @+ is signaling that you need to add a new id, the @ by itself tells the compiler to look for an existing id.